[changelog] update changelog for 6.0.0
[changelog] update changelog for 6.0.0

xalexec/javascript,naustudio/javascript,whichdigital/javascript-coding-standards,webcoding/javascript-style-guide,addshoppers/javascript,airbnb/javascript,LodoSoftware/javascript-style-guide,allanfish/javascript,cloudability/javascript-style-guide,bl00mber/javascript,codelegant/JavaScript,nulogy/javascript,ljharb/javascript,appcom-interactive/javascript,practicefusion/javascript,getjll/JavaScript-Style-Guide,LodoSoftware/javascript-style-guide,pokelondon/javascript,codelegant/JavaScript,naustudio/javascript